The apparatus disclosed herein is for performing x-ray examinations of the blood vessels and associated anatomy of the human body or, stated in another way, for performing angiographic procedures.
In general, apparatus that is designed especially for angiographic procedures, including both fluoroscopic viewing of the anatomy and recording of the images seen in various phases of the examination, must provide for angulating the axis of the x-ray beam from the frontal projection through a plurality of oblique projections to the lateral projection and through a plurality of head-to-foot angulations to at least 45.degree.-50.degree. in concert with the frontal and oblique angulations. The foregoing characterizes the class of diagnostic x-ray apparatus known as "multiaxis" angiographic apparatus.
During angiographic procedures, catheters, electrocardiograph leads and other devices are often connected to the patient. This makes is inconvenient for the x-ray technician working with the examining physician to move the patient and increases risk to the patient if gross movements are necessary. The desirability of being able to form most complete angiographic examinations which includes the views wherein the receptor is in close proximity (called contact) and those views wherein the receptor is at some greater distance from the patient (called magnification) without repositioning the patient or patient supporting table or hoisting the entire angulation apparatus on which the patient is supinely supported has been generally recognized, but until the apparatus disclosed herein was designed, this desirable objective has only been achieved at the expense of compromised x-ray source-to-image distance (SID) for magnification or contact angiography or both. If, as is the case with prior art angiographic apparatus, the patient must be raised or lowered significantly above or below normal x-ray table height to accommodate restrictions in the apparatus on positioning the x-ray source or receptors for the most advantageous x-ray view, the patient may then be in a position where it becomes inconvenient or awkward for the physician to work on the patient.
The apparatus disclosed herein is provided with one x-ray source and two image receptors, one of which is an x-ray image intensifier for examining the blood vessels fluoroscopically and the other of which is a radiographic film recording device such as a rapid film changer. The term "x-ray image intensifier" as used herein is intended to include any device that enables optical viewing of an x-ray image or, in other words, enables fluoroscopy to be performed. Maximum diagnostic information becomes available to the examining physician if the apparatus permits contact radiography and fluoroscopy and magnification radiography and fluoroscopy. In the magnification mode, the patient is customarily established about midway between the x-ray tube focal spot, which is the source, and the input plane of either the radiographic film or image intensifier. The focal spot-to-image receptor distance or SID for standard procedures is about 100 cm. This provides an image magnification factor of about 1.8 to 2.0. For contact radiography, where magnification is minimized, the intensifier or film changer input plane is moved closer to the body in which case it is desirable to maintain the same SID as is used in the magnification mode. The preference is, of course, to be able to make fluoroscopic examinations with the image intensifier and, alternatively, make film recordings by means of a film changer with minimum or maximum permissible magnification with rotational angulations from posterior-anterior (PA) through oblique views to lateral being accomplished rotationally about a point in space called the isocenter which is centered at the anatomical area of interest. There is existing multiaxial x-ray apparatus that has an image intensifier and a rapid film changer mounted on a gantry along with an x-ray tube for enabling obtaining fluoroscopic and radiographic images at various angular aspects. However, prior art apparatuses have various disadvantages such as, when a constant SID for various magnifications is desired, there must be movement of the isocenter away from the anatomical center of interest. Or, the movement of both the intensifier and the film changer radially with respect to the isocenter is not independent and, therefore a major realignment of the common receptor carriage is required in addition to interchanging the receptors.
In one prior art angiographic apparatus design, for example, two image receptors, namely a rapid film changer and an image intensifier are mounted in a cluster at one place on a gantry in spaced relationship to an x-ray source which is mounted at another place. Switching the image intensifier input plane and the film changer input plane into perpendicularity with the x-ray beam axis is accomplished by mounting the changer and intensifier on the same pivotal support. At one rotational position of the support, the x-ray beam axis will be perpendicular to the intensifier's image plane and will be parallel to the image plane of the film changer since the intensifier and film changer planes are at a right angle with respect to each other. At the other rotational position of the common support the image plane of the film changer is in perpendicularity with the x-ray beam axis while at the same time the image plane of the intensifier is in parallel with the beam axis and on the side of the beam. One disadvantage of the rotatable cluster design is that the image intensifier or film changer, when rotated, can strike the patient. Curved guards have been used to reduce the likelihood of doing injury to the patient and contact sensors should be used to lock the cluster against rotation if patient contact is made. In any event, it is preferable to lower the patient away from the cluster before rotating the receptors, to make sure the patient is cleared, and then restore the patient to the position in which the radiographic views are to be made. This extends a time for making a complete examination undesirably.
Another prior art angiographic apparatus design has an image intensifier mounted on a gantry for movement of its image plane perpendicular to the x-ray beam axis. A film changer is mounted on the gantry adjacent the intensifier for being moved linearly and into perpendicularity with the x-ray beam axis provided that the intensifier has been retracted axially. The apparatus which incorporates this feature, however, has its components, namely, the receptors and x-ray source physically related in such a manner that it is not possible to maintain the x-ray beam axis in perpendicularity with the image receptor planes for many of the angles in which the x-ray beam axis may be directed.
A significant disadvantage in prior art angiographic apparatus results from the manner in which the x-ray source and the image intensifier and film changer are mounted on the gantry for enabling interchange of the intensifier and changer. Prior art mounting schemes result in the gantry, or other structure which supports the image intensifier, changer and x-ray source, going out of balance when any of these components is moved to enable one or another of the operating modes. The fact that movement of a component causes severe unbalance requires that the gantry and the component on the gantry be driven by powerful motor drive systems that can overcome any amount of unbalance of the heavy load. Use of high power drive systems can result in injury if one of the components is driven into the patient. Hence, these systems require highly reliable sensing devices which cause the motors to stop before a patient becomes seriously compressed.